Mary meets Martha, a friendly housemaid. They gradually get to know each other. Martha tells Mary that there is a secret garden somewhere in the grounds, but it has been locked for years, and nobody knows where it is. Mary decides to find out. She meets gardener Ben Weatherstaff and his friend, a robin.
One day, the robin leads Mary to an ivy-covered wall. Here she discovers something lying in the earth. Is this something that will help her in her quest?